The present work reports on the properties of semi-interpenetrating networks (semi-IPN) based on chitosan and itaconic acid with poly(ethylene glycol) and poly(N-vinyl-2-pyrolidone) and hybrid polymer network (HPN) based on chitosan, itaconic acid and poly(vinyl alcohol) synthesized by polycondesation reaction, as well as the hydrogels of chitosan, itaconic and methacrylic acid (Ch/IA/MAA) synthesized by radical polymerization. All hydrogels were synthesized with varying monomer content and crosslinking agent concentration. The swelling kinetics was carried out in buffers of different pHs. Further, the samples were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), dynamic-mechanical analysis (DMA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).
The best system, determined by previous studies, Ch/IA/MAA hydrogels,

was applied as a sorbent for removal of heavy metals (Cu+2, Cd+2 and Zn+2) from aqueous solutions. The kinetics of metals adsorption was investigated, as well as the influence of pH, adsorbent dosage, temperature and concentration of metals on the degree of heavy metal removal. Also, the three most commonly used models of adsorption isotherms: Langmuir, Freundlich and Redlih-Peterson were applied. Afterwards, desorption of metals from sorbent were tested with appropriate reagents, with optimization of their concentration.
The results showed that the swelling of the synthesized hydrogels depend on the hydrogel composition, pH, temperature and degree of the crosslinking. The hydrogel composition and the degree of crosslinking affect the mechanical properties, as well as the type and content of the added polymer in the case of semi-IPN and HPN. SEM analysis showed that all hydrogels had a porous structure. Sorption of the metal ions led to reduction of the hydrogel pore size.
FT-IR analysis showed the ionic crosslinking between the COO-group of the acid and NH3+ groups of chitosan and chemical crosslinking between chitosan and poly(vinyl alcohol). Further, FT-IR analysis also showed that the metal is very likely bounded over –NH2 and –OH groups of chitosan and carboxyl groups originating from the incorporated acids. It was found that the adsorption capacity depend on the pH of solution, the adsorbent mass, initial solution metal concentration and temperature. The mechanism of Cd2+, Cu2+ and Zn2+ adsorption predominantly followed the pseudo-second order kinetics, while the best results were obtained for the Redlich-Peterson's model. Based on the adsorption activation energy the adsorption process is considered as a physisorption. Both HNO3 solutions, 0.1 mol/L and 0.01 mol/L, appeared to be effective for metal ions desorption (100.0 %). No significant loss of the capacity was observed during three cycles of adsorption-desorption.
According to the presented results, Ch/IA/MAA hydrogels could be used as sorbents for the removal of heavy metals (Cu+2, Cd+2 and Zn+2) from aqueous solutions due to their high adsorption capacity and the possibility of reuse, on account of complete recovery, which is very important for the practical application.